WHAT
Changes in the structure and shape of steel achieved through rolling, hammering, or stretching the steel at a low temperature (often room temperature).

WHY
To create a permanent increase in the hardness and strength of the steel.

HOW
The application of forces to the steel causes changes in the composition that enhance certain properties. In order for these improvements to be sustained, the temperature must be below a certain range, because the structural changes are eliminated by higher temperatures.